There are a number of implantable medical devices used for the repeated and prolonged access to a patients vascular system or other bodily conduits. Such devices include peripherally-inserted central catheters (“PICC's”), central venous catheters (“CVC's”), dialysis catheters, implantable ports, and midline infusion catheters. These devices are typically implanted into a patient for an extended period of time to allow for multiple treatments, such as the delivery of therapeutic agents or dialysis treatments. Use of such devices eliminates the need for multiple placements of single-use devices, thus reducing the risk of infection and placement complications, and reducing the overall cost of patient care. Examples of such implantable medical devices include BioFlo™ PICC's, Vaxcer® PICC's, Xcela® PICC's, and Vaxcel® Plus Chronic Dialysis catheters (all from AngioDynamics, Inc., Latham, N.Y.). Implantable devices such as these have distal sections that reside within the vasculature, and proximal sections that are typically outdwelling and include luers for connection to fluid sources and other medical devices.
Because these devices remain in a patient's body for an extended period of time, it is common practice to seal their proximal ends between uses to prevent blood loss and infection. Such a seal may be created with the use of a simple clamp placed on the catheter line (e.g. the Morpheus® SMART PICC, AngioDynamics, Inc., Latham, N.Y.), or with the use of an in-line valve such as that found in the Vaxcel® PICC with PASV® Valve Technology and described in U.S. Pat. Nos. 5,205,834 and 7,252,652, which are incorporated herein by reference. In-line valves are pressure activated such that they open to allow for fluid to be delivered through the valve upon the application of some threshold pressure, above which the valve will open, and below which the valve remains closed. Pressure activated valves may advantageously prevent patient complications and infections. In line catheter valves typically include a valve housing that defines a lumen (referred to as the “valve lumen”) and a valve element disposed across the valve lumen to regulate fluid flow. The valve element is normally closed, but opens in response to pressures above a pre-defined threshold. Valve elements used in in-line catheter valves are typically flexible slitted membranes such as those disclosed in U.S. Pat. No. 5,843,044, which is incorporated by reference herein.
It is often desirable to measure fluid pressures such as blood pressure or central venous pressure through a catheter. It may also be desirable to measure an ECG signal through a column of saline extending from a distal catheter tip to a proximal extension tube and luer. In the case of valved devices, however, the in-line valve inhibits transmission of fluid pressure from the distal catheter tip to the proximal luer. Current practice is to insert an elongated instrument through the valve element (typically a slitted membrane), but the insertion of elongated tools into the valve lumen to measure blood pressure raises a risk of puncturing the membrane or tearing, weakening, or otherwise permanently deforming the membrane or its slits. Additionally, excessive displacement of the edges of slit raises the risk that the edges will not return to their fully closed, fully and flushly apposed positions, instead returning to a folded or puckered position, and that gaps or edges may exist through which fluids may leak, potentially leading to thrombosis and/or infection. Accordingly, there is a need for systems that permit the measurement of blood pressure through catheters having in-line valves, preferably without the risk of damaging the valve element.